Fuel cell systems generate electric power, using hydrogen-containing gas as a fuel and air as an oxidizing gas. Since there is no infrastructure for supplying hydrogen which is put in place, a hydrogen generator having a reformer is generally used for generating hydrogen-containing gas through a reforming reaction in which natural gas, LPG or the like is used as a raw material.
As the reforming reaction, various methods such as partial oxidation reforming, autothermal reforming and steam reforming are known. The steam reforming reaction, for example, occurs between natural gas serving as a raw material and water vapor in the presence of a Ni or Ru precious-metal-based reforming catalyst at high temperatures of about 600 to 700° C., so that hydrogen-containing gas, which contains hydrogen as a main component, is yielded.
The material gas such as natural gas contains sulfuric compounds which are required to be removed with some sort of method because they are poisoning substances particularly to the reforming catalyst. One known technique for removing the sulfuric compounds is a hydrodesulfurization method that utilizes recycled hydrogen-containing gas.
There has heretofore been proposed a hydrogen generator according to which a recycle flow passage for recycling the hydrogen-containing gas is provided with a temperature detector that detects occurrence of a clogging in the recycle flow passage (see e.g., Patent Literature 1).